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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: CALET Gamma-Ray Burst Monitor detection
  2. GRB 250311B: SVOM detection of a burst
  3. GRB 250309B: SVOM/VT optical observation
  4. GRB 250311A/MAXI J1457-026: MAXI/GSC detection
  5. The EP-WXT trigger 01709132425 is not a real source
  6. GRB 250309B / AT2025dws: further SAO RAS optical observations
  7. IceCube-250309A: Upper limits from Fermi-GBM Observations
  8. EP250308a: 1.6m Mephisto optical upper limits
  9. Konus-Wind detection of GRB 250309B
  10. GRB 250309B / AT2025dws: KMTNet-CTIO optical observations
  11. IPN triangulation of GRB 250308A (short)
  12. IPN triangulation of GRB 250309B
  13. IceCube-241224A: MASTER detection of PKS 1217+02 blazar flare with Zhirkov effect
  14. GRB 250309B/AT2025dws : COLIBRÍ Detection of the Optical Counterpart
  15. GRB 250309B: Swift-XRT refined Analysis
  16. GRB 250309B / IceCube-250309A: GECAM-B observations
  17. GRB 250309B / AT2025dws: OSIRIS+/GTC spectroscopy z=1.898
  18. Liverpool Telecope observations of AT 2025dws / GRB 250309B
  19. GRB 250309B / AT2025dws: SAO RAS optical observations
  20. GRB 250309B / AT2025dws: Swift-UVOT detection
  21. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  22. GRB 250309B: Fermi GBM Observation
  23. Fermi GRB 250309B: Global MASTER-Net observations report
  24. Fermi GRB 250309A: Global MASTER-Net observations report
  25. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  26. IceCube-250309A: No candidates from the Zwicky Transient Facility
  27. Fermi-LAT gamma-ray observations of IceCube-250309A
  28. GRB 250308A: SVOM/GRM detection of QPO in the tail emission
  29. GRB 250309B: Fermi GBM Final Localization
  30. Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
  31. GRB 230509B: Tiled Swift observations
  32. GRB 250308A: SVOM/GRM observation of a bright short burst
  33. IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
  34. IceCube Alert 250309.32: Global MASTER-Net observations report
  35. GRB 250309B: BALROG localization (Fermi Trigger 763198715 / GRB 250309318)
  36. EP250308a: Global MASTER-Net observations report
  37. EP250308a: GSP optical upper limit
  38. EP250308a: FTW optical and NIR upper limits
  39. EP250308a: Einstein Probe detection of an X-ray transient
  40. EP250308a: NOT optical upper limit
  41. GRB 250309A: Fermi GBM Final Real-time Localization
  42. GRB 250306A: EIRSAT-1 GMOD detection
  43. The EP-WXT trigger 01709132387 is likely a flaring star
  44. Fermi GRB 250307A: Global MASTER-Net observations report
  45. Konus-Wind detection of GRB 250306A
  46. GRB 250307A: Fermi GBM Final Real-time Localization
  47. GRB 250306A: Swift-BAT refined analysis
  48. GRB 250306A: NuSTAR detection of the prompt emission
  49. EP250304a: MeerKAT detection of a possible radio counterpart
  50. IceCube-241016A: MASTER flaring blazar 5BZU J073038.29-320820.2 with Zhirkov effect
  51. GRB 250305A: AstroSat CZTI detection
  52. EP250302a:Xinglong optical observations
  53. GRB 250306A: AstroSat CZTI detection
  54. Fermi trigger No 762963055: Global MASTER-Net observations report
  55. Fermi Gamma-ray Burst Monitor trigger 762963055/250306591 is not a GRB
  56. Swift GRB 250306A: Global MASTER-Net observations report
  57. LIGO/Virgo/KAGRA S250207bg: Update-5 NED Galaxies in the Localization Volume
  58. GRB 250306A: Swift detection of a burst
  59. LIGO/Virgo/KAGRA S250207bg: Updated Sky localization
  60. GRB250101A: Radio upper limits from VLA observations
  61. LIGO/Virgo/KAGRA S250306ej: Retraction of GW compact binary merger candidate
  62. GRB 250305A: SVOM/GRM observation of a burst
  63. The EP-WXT trigger 01709132323 is likely a flaring star
  64. EP250304A: Upper limits from Fermi-GBM Observations
  65. Fermi GRB 250305A: Global MASTER-Net observations report
  66. Fermi-LAT Gamma-ray Observations of IceCube-250302A
  67. GRB 250305A: Fermi GBM Final Real-time Localization
  68. EP250302a: Optical Observations at CrAO and SAO RAS
  69. GRB 250219A: SVOM/C-GFT optical upper limit at early phase
  70. EP 250304A: Optical counterpart detection by LCO
  71. EP250302A: 1.3m DFOT optical afterglow detection
  72. IceCube-250302A: Upper limits from a search for additional neutrino events in IceCube
  73. EP250304a: refined analysis of the EP-WXT and EP-FXT observations
  74. Konus-Wind detection of GRB 250222A
  75. EP250304a: REM NIR upper limits
  76. IPN triangulation of GRB 250222A
  77. EP250304a: Swift/UVOT detection of an optical counterpart with a rising light curve
  78. EP250302a: Mondy Continued Optical Observations
  79. EP250304a: VLT/X-shooter redshift z = 0.200
  80. EP250304a: Swift-XRT detection of a fading X-ray source
  81. EP250304a: TRT optical counterpart detection
  82. LIGO/Virgo/KAGRA S250304cb: Identification of a GW compact binary merger candidate
  83. EP250304a: Global MASTER-Net observations report
  84. EP250304a: Einstein Probe detection of an X-ray transient
  85. The EP-WXT trigger 01709132212 is not a real source
  86. EP250302a: SVOM/VT optical observation
  87. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Swift/UVOT Upper Limits
  88. EP250302a: SAO RAS optical observations
  89. EP250302a : GIT optical follow-up
  90. EP250302a: VLT/X-shooter redshift confirmation
  91. EP250225a: the candidate optical counterpart is an AGN
  92. EP250302a: Kinder optical follow-up observations
  93. LIGO/Virgo/KAGRA S250302av: 2 counterpart neutrino candidate events from an IceCube neutrino search
  94. EP250302a: Swift/UVOT detection
  95. EP250302a: NUTTelA-TAO Early Measurments
  96. EP250302a: optical observation from the INAF Asiago Observatory
  97. EP250302a: REM NIR upper limits
  98. IceCube-241113A: MASTER flaring blazar 5BZB J1311+0853 with Zhirkov effect
  99. EP250302a: Mondy Observations and Optical Light Curve
  100. EP250302a: VLT/MUSE optical redshift z = 1.131

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