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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"
  1. GRB 250308A: SVOM/GRM detection of QPO in the tail emission
  2. GRB 250309B: Fermi GBM Final Localization
  3. Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
  4. GRB 230509B: Tiled Swift observations
  5. GRB 250308A: SVOM/GRM observation of a bright short burst
  6. IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
  7. IceCube Alert 250309.32: Global MASTER-Net observations report
  8. GRB 250309B: BALROG localization (Fermi Trigger 763198715 / GRB 250309318)
  9. EP250308a: Global MASTER-Net observations report
  10. EP250308a: GSP optical upper limit
  11. EP250308a: FTW optical and NIR upper limits
  12. EP250308a: Einstein Probe detection of an X-ray transient
  13. EP250308a: NOT optical upper limit
  14. GRB 250309A: Fermi GBM Final Real-time Localization
  15. GRB 250306A: EIRSAT-1 GMOD detection
  16. The EP-WXT trigger 01709132387 is likely a flaring star
  17. Fermi GRB 250307A: Global MASTER-Net observations report
  18. Konus-Wind detection of GRB 250306A
  19. GRB 250307A: Fermi GBM Final Real-time Localization
  20. GRB 250306A: Swift-BAT refined analysis
  21. GRB 250306A: NuSTAR detection of the prompt emission
  22. EP250304a: MeerKAT detection of a possible radio counterpart
  23. IceCube-241016A: MASTER flaring blazar 5BZU J073038.29-320820.2 with Zhirkov effect
  24. GRB 250305A: AstroSat CZTI detection
  25. EP250302a:Xinglong optical observations
  26. GRB 250306A: AstroSat CZTI detection
  27. Fermi trigger No 762963055: Global MASTER-Net observations report
  28. Fermi Gamma-ray Burst Monitor trigger 762963055/250306591 is not a GRB
  29. Swift GRB 250306A: Global MASTER-Net observations report
  30. LIGO/Virgo/KAGRA S250207bg: Update-5 NED Galaxies in the Localization Volume
  31. GRB 250306A: Swift detection of a burst
  32. LIGO/Virgo/KAGRA S250207bg: Updated Sky localization
  33. GRB250101A: Radio upper limits from VLA observations
  34. LIGO/Virgo/KAGRA S250306ej: Retraction of GW compact binary merger candidate
  35. GRB 250305A: SVOM/GRM observation of a burst
  36. The EP-WXT trigger 01709132323 is likely a flaring star
  37. EP250304A: Upper limits from Fermi-GBM Observations
  38. Fermi GRB 250305A: Global MASTER-Net observations report
  39. Fermi-LAT Gamma-ray Observations of IceCube-250302A
  40. GRB 250305A: Fermi GBM Final Real-time Localization
  41. EP250302a: Optical Observations at CrAO and SAO RAS
  42. GRB 250219A: SVOM/C-GFT optical upper limit at early phase
  43. EP 250304A: Optical counterpart detection by LCO
  44. EP250302A: 1.3m DFOT optical afterglow detection
  45. IceCube-250302A: Upper limits from a search for additional neutrino events in IceCube
  46. EP250304a: refined analysis of the EP-WXT and EP-FXT observations
  47. Konus-Wind detection of GRB 250222A
  48. EP250304a: REM NIR upper limits
  49. IPN triangulation of GRB 250222A
  50. EP250304a: Swift/UVOT detection of an optical counterpart with a rising light curve
  51. EP250302a: Mondy Continued Optical Observations
  52. EP250304a: VLT/X-shooter redshift z = 0.200
  53. EP250304a: Swift-XRT detection of a fading X-ray source
  54. EP250304a: TRT optical counterpart detection
  55. LIGO/Virgo/KAGRA S250304cb: Identification of a GW compact binary merger candidate
  56. EP250304a: Global MASTER-Net observations report
  57. EP250304a: Einstein Probe detection of an X-ray transient
  58. The EP-WXT trigger 01709132212 is not a real source
  59. EP250302a: SVOM/VT optical observation
  60. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Swift/UVOT Upper Limits
  61. EP250302a: SAO RAS optical observations
  62. EP250302a : GIT optical follow-up
  63. EP250302a: VLT/X-shooter redshift confirmation
  64. EP250225a: the candidate optical counterpart is an AGN
  65. EP250302a: Kinder optical follow-up observations
  66. LIGO/Virgo/KAGRA S250302av: 2 counterpart neutrino candidate events from an IceCube neutrino search
  67. EP250302a: Swift/UVOT detection
  68. EP250302a: NUTTelA-TAO Early Measurments
  69. EP250302a: optical observation from the INAF Asiago Observatory
  70. EP250302a: REM NIR upper limits
  71. IceCube-241113A: MASTER flaring blazar 5BZB J1311+0853 with Zhirkov effect
  72. EP250302a: Mondy Observations and Optical Light Curve
  73. EP250302a: VLT/MUSE optical redshift z = 1.131
  74. INTEGRAL: end of scientific operations
  75. EP250302A: VLT near-infrared observations
  76. EP250302A: VLT/X-shooter tentative redshift
  77. EP250302a: OHP/T193 optical and spectroscopic observations
  78. EP250302a: Global MASTER-Net observations report
  79. EP250302a: Xinglong F60B optical observation
  80. EP250302a: Swift-XRT observations of a fading X-ray source
  81. EP250302a: Einstein Probe detection of an X-ray transient
  82. EP250302a: SVOM/C-GFT optical observations
  83. GRB 250226A: GRANDMA Optical Observations
  84. EP250302a: Montarrenti Observatory optical detection
  85. Fermi GRB 250302A: Global MASTER-Net observations report
  86. EP250302a: FTW optical and NIR detection
  87. EP250302a: Nanshan/HMT optical counterpart detection
  88. IceCube-250302A - IceCube observation of a high-energy neutrino candidate track-like event
  89. GRB 250302A: Fermi GBM Final Real-time Localization
  90. GRB 250228A: Fermi GBM Final Localization
  91. The EP-WXT trigger 01709132140 is likely a flaring star
  92. LIGO/Virgo/KAGRA S250206dm: early X-ray upper limits from Einstein Probe WXT and preliminary results of FXT observations
  93. GRB 250225B: VLT near-infrared afterglow confirmation
  94. EP250228a: Optical observations with Kinder and Swift/UVOT
  95. Konus-Wind detection of GRB 250226A
  96. GRB 250225B: EIRSAT-1 GMOD Detection
  97. GRB 250226A: KAO Optical Upper Limit
  98. GRB 250226A: AbAO AS-32 Optical Upper Limit
  99. EP250227a: Global MASTER-Net observations report
  100. EP250223A: Upper limits from Fermi-GBM Observations

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