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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"

31635 results found.

  1. GRB 250309B / AT2025dws: KMTNet-CTIO optical observations
  2. IPN triangulation of GRB 250308A (short)
  3. IPN triangulation of GRB 250309B
  4. IceCube-241224A: MASTER detection of PKS 1217+02 blazar flare with Zhirkov effect
  5. GRB 250309B/AT2025dws : COLIBRÍ Detection of the Optical Counterpart
  6. GRB 250309B: Swift-XRT refined Analysis
  7. GRB 250309B / IceCube-250309A: GECAM-B observations
  8. GRB 250309B / AT2025dws: OSIRIS+/GTC spectroscopy z=1.898
  9. Liverpool Telecope observations of AT 2025dws / GRB 250309B
  10. GRB 250309B / AT2025dws: SAO RAS optical observations
  11. GRB 250309B / AT2025dws: Swift-UVOT detection
  12. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  13. GRB 250309B: Fermi GBM Observation
  14. Fermi GRB 250309B: Global MASTER-Net observations report
  15. Fermi GRB 250309A: Global MASTER-Net observations report
  16. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  17. IceCube-250309A: No candidates from the Zwicky Transient Facility
  18. Fermi-LAT gamma-ray observations of IceCube-250309A
  19. GRB 250308A: SVOM/GRM detection of QPO in the tail emission
  20. Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
  21. GRB 230509B: Tiled Swift observations
  22. IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
  23. EP250308a: Global MASTER-Net observations report
  24. EP250308a: GSP optical upper limit
  25. GRB 250306A: EIRSAT-1 GMOD detection
  26. Fermi GRB 250307A: Global MASTER-Net observations report
  27. Konus-Wind detection of GRB 250306A
  28. GRB 250306A: Swift-BAT refined analysis
  29. GRB 250306A: NuSTAR detection of the prompt emission
  30. EP250304a: MeerKAT detection of a possible radio counterpart
  31. IceCube-241016A: MASTER flaring blazar 5BZU J073038.29-320820.2 with Zhirkov effect
  32. GRB 250305A: AstroSat CZTI detection
  33. EP250302a:Xinglong optical observations
  34. GRB 250306A: AstroSat CZTI detection
  35. Swift GRB 250306A: Global MASTER-Net observations report
  36. LIGO/Virgo/KAGRA S250207bg: Updated Sky localization
  37. GRB250101A: Radio upper limits from VLA observations
  38. GRB 250305A: SVOM/GRM observation of a burst
  39. EP250304A: Upper limits from Fermi-GBM Observations
  40. Fermi GRB 250305A: Global MASTER-Net observations report
  41. Fermi-LAT Gamma-ray Observations of IceCube-250302A
  42. EP250302a: Optical Observations at CrAO and SAO RAS
  43. GRB 250219A: SVOM/C-GFT optical upper limit at early phase
  44. EP 250304A: Optical counterpart detection by LCO
  45. EP250302A: 1.3m DFOT optical afterglow detection
  46. IceCube-250302A: Upper limits from a search for additional neutrino events in IceCube
  47. EP250304a: refined analysis of the EP-WXT and EP-FXT observations
  48. Konus-Wind detection of GRB 250222A
  49. EP250304a: REM NIR upper limits
  50. IPN triangulation of GRB 250222A
  51. EP250304a: Swift/UVOT detection of an optical counterpart with a rising light curve
  52. EP250302a: Mondy Continued Optical Observations
  53. EP250304a: VLT/X-shooter redshift z = 0.200
  54. EP250304a: Swift-XRT detection of a fading X-ray source
  55. EP250304a: TRT optical counterpart detection
  56. LIGO/Virgo/KAGRA S250304cb: Identification of a GW compact binary merger candidate
  57. EP250304a: Global MASTER-Net observations report
  58. EP250302a: SVOM/VT optical observation
  59. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Swift/UVOT Upper Limits
  60. EP250302a: SAO RAS optical observations
  61. EP250302a : GIT optical follow-up
  62. EP250302a: VLT/X-shooter redshift confirmation
  63. EP250225a: the candidate optical counterpart is an AGN
  64. EP250302a: Kinder optical follow-up observations
  65. EP250302a: Swift/UVOT detection
  66. EP250302a: NUTTelA-TAO Early Measurments
  67. EP250302a: optical observation from the INAF Asiago Observatory
  68. EP250302a: REM NIR upper limits
  69. IceCube-241113A: MASTER flaring blazar 5BZB J1311+0853 with Zhirkov effect
  70. EP250302a: Mondy Observations and Optical Light Curve
  71. EP250302a: VLT/MUSE optical redshift z = 1.131
  72. INTEGRAL: end of scientific operations
  73. EP250302A: VLT near-infrared observations
  74. EP250302A: VLT/X-shooter tentative redshift
  75. EP250302a: OHP/T193 optical and spectroscopic observations
  76. EP250302a: Global MASTER-Net observations report
  77. EP250302a: Xinglong F60B optical observation
  78. EP250302a: Swift-XRT observations of a fading X-ray source
  79. EP250302a: Einstein Probe detection of an X-ray transient
  80. EP250302a: SVOM/C-GFT optical observations
  81. GRB 250226A: GRANDMA Optical Observations
  82. EP250302a: Montarrenti Observatory optical detection
  83. Fermi GRB 250302A: Global MASTER-Net observations report
  84. EP250302a: FTW optical and NIR detection
  85. LIGO/Virgo/KAGRA S250206dm: early X-ray upper limits from Einstein Probe WXT and preliminary results of FXT observations
  86. GRB 250225B: VLT near-infrared afterglow confirmation
  87. EP250228a: Optical observations with Kinder and Swift/UVOT
  88. Konus-Wind detection of GRB 250226A
  89. GRB 250225B: EIRSAT-1 GMOD Detection
  90. GRB 250226A: KAO Optical Upper Limit
  91. GRB 250226A: AbAO AS-32 Optical Upper Limit
  92. EP250227a: Global MASTER-Net observations report
  93. EP250223A: Upper limits from Fermi-GBM Observations
  94. EP250227a: TRT optical upper limit
  95. GRB 250225B: VLT/HAWKI near-infrared observations
  96. EP250227a: Optical upper limits with Kinder observations
  97. EP250227a: NOT optical observations
  98. EP250228a: updates on the EP observations
  99. GRB 250226A: Fermi GBM Observation
  100. EP250225a: EP-FXT follow-up observation

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