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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 250704A: SVOM detection of a burst
  2. GRB 250702F: Swift/UVOT Detection
  3. GRB 250702A: CALET Gamma-Ray Burst Monitor detection
  4. Fermi GBM Analysis of GRB 250702B (formerly B,D,E); dissociation of C burst
  5. Fermi GRB 250703A: Global MASTER-Net observations report
  6. GRBs 250702B,C,D,E / EP250702a: 2.2m CAHA optical upper limit
  7. GRB 250702F: Swift-XRT refined Analysis
  8. GRB 250702F: Fermi GBM Observation
  9. GRB 250702F: Leavitt Observatory optical observations
  10. GRB 250702F: AKO Optical Afterglow Detection
  11. GRBs 250702B,C,D,E / EP250702a: VLT/HAWK-I NIR candidate
  12. GRBs 250702B,C,D,E / EP250702a: SVOM/GRM observation
  13. GRB 250702A: GECAM-B detection
  14. GRB 250702F: Skynet Optical Observations
  15. GRB 250424A: VIRT Optical Upper Limit
  16. GRBs 250702B/C/D/E / EP250702a: Swift XRT localization
  17. GRB 250702B,C,D,E/EP250702a: COLIBRÍ optical upper limit
  18. EP250702a/GRB 250702B, C, D, E: EP-FXT follow-up observation
  19. GRB 250702F: TRT Optical Observation
  20. GRB 250703A: DDOTI Optical Upper Limit
  21. GRBs 250702B,C,D,E / EP250702a: Konus-Wind detection of a hard X-ray transient activity
  22. GRB 250702F: REM optical afterglow detection
  23. EP250702a: Global MASTER-Net observations report
  24. GRB 250702F: DDOTI Optical Observation
  25. GRB 250702B,C,D,E / EP 250702a: MAXI/GSC detection
  26. GRB 250703A: Fermi GBM Final Real-time Localization
  27. EP250702a/GRB 250702B,C,D,E: GOTO optical upper limits
  28. GRB 250702F: COLIBRÍ Observations of the Afterglow
  29. EP250702a : an X-ray transient detected by Einstein Probe likely associated with GRB 250702B,C,D,E
  30. Fermi GRB 250702E: Global MASTER-Net observations report
  31. Fermi GRB 250702B: Global MASTER-Net observations report
  32. GRB 250702D, C, E: Swift/BAT-GUANO localization skymap of a burst or galactic transient
  33. GRB 250702F: Enhanced Swift-XRT position
  34. GRB 250702F: GTC/OSIRIS+ spectroscopic redshift z = 1.520
  35. GRB 250702F: NOT observations of the optical afterglow
  36. GRB 250702F: MASTER optical afterglow observation
  37. Fermi GRB 250702F: Global MASTER-Net observations report
  38. Fermi GRB 250702C: Global MASTER-Net observations report
  39. GRB 250702F: GOTO optical counterpart detection
  40. GRB 250702F: Ondrejov D50 optical afterglow detection
  41. GRB 250702F: Swift detection of a burst with an optical counterpart
  42. Swift GRB 250702F: Global MASTER-Net observations report
  43. GRB 250702F: Fermi GBM Final Real-time Localization
  44. Fermi GBM Triggers 250702B, C, D and E are likely from the same source
  45. GRB 250702E: Fermi GBM Final Real-time Localization
  46. Konus-Wind detection of GRB 250627A
  47. IPN triangulation of GRB 250627A (short)
  48. GRB 250702A: Fermi GBM Detection
  49. GRB 250702D: Fermi GBM Final Localization Correction
  50. GRB 250702C: Fermi GBM Final Real-time Localization
  51. LIGO/Virgo/KAGRA S250702n: Identification of a GW compact binary merger candidate
  52. GRB 250702B: Fermi GBM Final Real-time Localization
  53. GRB 250702A: BALROG localization (Fermi Trigger 773142852 / GRB 250702413)
  54. GRB 250702A: Fermi GBM Final Real-time Localization
  55. LIGO/Virgo/KAGRA S250701bq: Identification of a GW compact binary merger candidate
  56. LIGO/Virgo/KAGRA S250701bp: Identification of a GW compact binary merger candidate
  57. Fermi Gamma-ray Burst Monitor trigger 772838080/250628885 is not a GRB
  58. GRB 250628B: Swift-XRT observations
  59. Fermi Gamma-ray Burst Monitor trigger 772981768/250630548 is not a GRB
  60. GRB 250628B: SVOM/VT optical upper limit
  61. GRB 250628B: EP-FXT counterpart detection
  62. LIGO/Virgo/KAGRA S250629bs: Updated Sky localization
  63. GRB 250627A: Insight-HXMT detection
  64. GRB 250627A: SVOM/GRM detection of a short burst
  65. LIGO/Virgo/KAGRA S250629ae: Updated Sky localization
  66. LIGO/Virgo/KAGRA S250629bs: Identification of a GW compact binary merger candidate
  67. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate (duplicate submission)
  68. LIGO/Virgo/KAGRA S250629ae: Identification of a GW compact binary merger candidate
  69. LIGO/Virgo/KAGRA S250628am: Updated Sky localization
  70. GRB 250628A: REM optical/NIR upper limits
  71. GRB 250628C: Fermi GBM Final Real-time Localization
  72. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate
  73. GRB 250628B: SVOM detection of a long burst
  74. Fermi Gamma-ray Burst Monitor trigger 772811638/250628579 is not a GRB
  75. GRB 250625A: VLT/X-shooter spectroscopic observations at the afterglow position
  76. GRB 250628A: VLT/X-shooter upper limits
  77. GRB 250628A: Swift/UVOT Upper Limits
  78. GRB 250628A: Swift-XRT refined Analysis
  79. Fermi GRB 250626A: Global MASTER-Net observations report
  80. Swift GRB 250628A: Global MASTER-Net observations report
  81. GRB 250628A: Enhanced Swift-XRT position
  82. GRB 250628A: Swift detection of a burst
  83. GRB 250625A: Swift-BAT refined analysis
  84. GRB 250625A: Leavitt Observatory afterglow detection
  85. Fermi Gamma-ray Burst Monitor trigger 772732642/250627665 is not a GRB
  86. Fermi Gamma-ray Burst Monitor trigger 772720540/250627525 is not a GRB
  87. GRB 250625A: AbAO and INASAN Kislovodsk Optical Observations
  88. The EP-WXT trigger 01709179435 is likely a new outburst of the CV SS Cyg
  89. GRB 250625A: GTC/OSIRIS+ spectroscopic observations of the potential host galaxy
  90. GRB 250626A: Fermi GBM Final Real-time Localization
  91. Fermi Gamma-ray Burst Monitor trigger 772647532/250626680 is not a GRB
  92. GRB 250625A: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  93. GRB 250625A: SVOM/C-GFT upper limit in early phase
  94. GRB 250625A: GECAM-B detection
  95. GRB 250625A: Swift/UVOT Upper Limits
  96. GRB 250625A: ABObservatory afterglow detection
  97. GRB 250625A: OHP/T193 optical detection
  98. GRB 250625A: COLIBRÍ optical observations
  99. GRB 250625A: Fermi-LAT detection
  100. GRB 250625A: Swift-XRT refined Analysis

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