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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

8474 results found.

  1. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 1)
  2. LIGO/Virgo/KAGRA S250329fl: 2 counterpart neutrino candidate events from an IceCube neutrino search
  3. GRB 250329A: Swift-XRT afterglow detection
  4. GRB 250328A: SVOM/VT optical observation
  5. GRB 250328A: SVOM/COLIBRÍ (F-GFT) optical afterglow candidate
  6. GRB 250328A: VLT/HAWK-I near-infrared afterglow candidate
  7. GRB 250329A: VLT/X-shooter redshift z = 2.921
  8. GRB 250329A: SVOM/VT optical counterpart confirmation
  9. GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate
  10. LIGO/Virgo/KAGRA S250328ae: NED Galaxies in the 4-Update Localization Volume
  11. EP250315a: Pan-STARRS r and i-band imaging and photometry
  12. LIGO/Virgo/KAGRA S250328ae: Updated Sky localization
  13. LIGO/Virgo/KAGRA S250328ae: Identification of a GW compact binary merger candidate
  14. GRB 250327B: 1.6m Mephisto optical observations
  15. GRB 250327B: SVOM/VT optically bright counterpart
  16. GRB 250327B: SAO RAS optical candidate
  17. GRB 250327A: SVOM/VT optical candidate
  18. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  19. LIGO/Virgo/KAGRA S250326y: Updated Sky localization
  20. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  21. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  22. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  23. GRB 250322A: further NOT optical observations
  24. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  25. GRB 250322A: Gemini-North redshift of candidate host galaxy
  26. GRB 250322A: VLT optical observations
  27. GRB 250322A: VLT near-infrared observations
  28. GRB 250322A: NOT optical upper limits
  29. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  30. GRB 250322A: Swift detection of a short burst
  31. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  32. GRB 250321B: Swift ToO observations
  33. GRB 250321B: SVOM detection of a sub-threshold transient event
  34. EP250321a: Kinder optical follow-up observations
  35. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  36. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  37. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  38. GRB 250309B/AT2025dws: further ATCA observations
  39. GRB 250316A: AbAO AS-32 Optical Upper Limit
  40. GRB 250317B: SVOM/VT detection of an optical candidate from VHF data
  41. GRB 250316A: Swift ToO observations
  42. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  43. GRB 250314A: EP-FXT afterglow detection
  44. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  45. EP250315a: optical counterpart candidate detected by Gemini North
  46. GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
  47. GRB 250314A: SVOM/VT upper limit
  48. GRB 250314A: NOT near-infrared candidate counterpart
  49. GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
  50. GRB 250313A: Swift ToO observations
  51. EP250304a: Pan-STARRS r and i-band imaging and photometry
  52. LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
  53. GRB 250312A: Swift detection of a burst
  54. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  55. IceCube-250309A: Upper limits from a search for additional neutrino events in IceCube
  56. GRB 250311A: Tiled Swift observations
  57. GRB 250309B: SVOM/VT optical observation
  58. GRB 250309B / AT2025dws: further SAO RAS optical observations
  59. IceCube-250309A: Upper limits from Fermi-GBM Observations
  60. Konus-Wind detection of GRB 250309B
  61. GRB 250309B/AT2025dws : COLIBRÍ Detection of the Optical Counterpart
  62. GRB 250309B / IceCube-250309A: GECAM-B observations
  63. GRB 250309B / AT2025dws: Swift-UVOT detection
  64. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  65. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  66. IceCube-250309A: No candidates from the Zwicky Transient Facility
  67. GRB 230509B: Tiled Swift observations
  68. IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
  69. The EP-WXT trigger 01709132387 is likely a flaring star
  70. LIGO/Virgo/KAGRA S250207bg: Update-5 NED Galaxies in the Localization Volume
  71. LIGO/Virgo/KAGRA S250207bg: Updated Sky localization
  72. LIGO/Virgo/KAGRA S250306ej: Retraction of GW compact binary merger candidate
  73. EP250304A: Upper limits from Fermi-GBM Observations
  74. IceCube-250302A: Upper limits from a search for additional neutrino events in IceCube
  75. LIGO/Virgo/KAGRA S250304cb: Identification of a GW compact binary merger candidate
  76. EP250225a: the candidate optical counterpart is an AGN
  77. EP250302a: Kinder optical follow-up observations
  78. LIGO/Virgo/KAGRA S250302av: 2 counterpart neutrino candidate events from an IceCube neutrino search
  79. EP250302a: Montarrenti Observatory optical detection
  80. IceCube-250302A - IceCube observation of a high-energy neutrino candidate track-like event
  81. GRB 250225B: VLT near-infrared afterglow confirmation
  82. EP250228a: Optical observations with Kinder and Swift/UVOT
  83. EP250223A: Upper limits from Fermi-GBM Observations
  84. GRB 250225B: VLT/HAWKI near-infrared observations
  85. EP250227a: Optical upper limits with Kinder observations
  86. EP250225a: EP-FXT follow-up observation
  87. LIGO/Virgo/KAGRA S250227e: Updated Sky localization
  88. LIGO/Virgo/KAGRA S250226dl: Updated Sky localization
  89. GRB 250225B: VLT/Xshooter imaging
  90. GRB 250205A / EP250205A: further radio observations with the VLA
  91. EP250225a: NOT optical candidate counterpart
  92. EP250226a/GRB 250226A: 1.6m Mephisto observations
  93. LIGO/Virgo/KAGRA S250206dm: Upper limits from SVOM/GRM Observations
  94. EP250226a/GRB 250226A: Kinder optical follow-up observations
  95. LIGO/Virgo/KAGRA S250223dk: Insight-HXMT/HE sub-threshold detection of a burst (HEB 250223501)
  96. LIGO/Virgo/KAGRA S250227y: Retraction of GW compact binary merger candidate
  97. LIGO/Virgo/KAGRA S250227e: Identification of a GW compact binary merger candidate
  98. LIGO/Virgo/KAGRA S250226dl: Identification of a GW compact binary merger candidate
  99. GRB 250225B: REM NIR upper limits
  100. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event

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